Amplifier system



p 1933. A. K. ROSS 1,926,860

AMPLIFIER SYSTEM Filed April 25, 1 2

I INVENTOR ATTORNEY Patented Sept. 12, 1933 UNITED PAT AMPLIFIER SYSTEMAllan K. .Ross, Rochester, N. Y. Application April 25, 1925.}Serial No.25,780

5 Claims. (01. 250- 40 This invention relates to amplifier systems andin particular to amplifier'systems foruse. in amplifying radio signals.v.

In certain types of amplifier systems it has been customary to employaplurality of tuned amplifying stages. gives excellent results, isexpensive to manufacture since it requires a variable condenser for 1each stagerwith the result that there'are at least 7 as many controls asthere are amplifying stages,

over a wide portion of the range of frequencies the stages are not inresonance so that accurate tuning does not take place. In order toovercome this ditficulty it has been proposed to provide one mastercontrol for roughly tuning each of a plurality of stages, and furtherto, provide an individual. Vernier control for the'accurate tu'ningofeach stage. The necessity for such Vernier controls defeats the purposeof such a master control arrangement.

In accordance with the present invention it is proposed'to obviate thenecessity of providing a variable condenser and an individual controltherefor in each, amplifying stage and to avoid the undesirable featuresof the master controlled system by providing a single variable capacitycommon to a plurality of amplifying stages whereby all of the stages maybe simultaneously and accurately tuned by the use of a single control.

The drawing represents the invention applied to a tuned radio frequencyamplifying radio re ceiver, although it will be understood that it maybe used with audio amplifying systems or in any other arrangementwherein a plurality of stages are tuned to the same or to anapproximately:

the input circuit of a thermionic device or vac-' .uum tube 8. Thisinput circuit extends from 5 the grid 9 of this vacuum tube throughv thesec- Such an arrangement, while it conductor 17 to the filament 23.

, ondary'winding '7, the potentiometer 10 to the filament 11. with thecommon variable condenser .13 is con-' The fixedcondenser 12 in seriesnected in multiple across the input circuit and p the capacity of thefixed'condenser 12 with that of the variable condenser 13 and theinductance of the secondary coil '7 serve to tune the input circuit justdescribed. The output circuit of the thermionic device 8 extendsfromtheplate 14 thereof through the primary winding 15 'of a secondradio "frequency transformer throughthe high potential B battery 16 andcommon conductor 17Ito the filament system including the low voltage Abattery 18 by which the filaments of the various thermionic devices areheated.

The primary winding 15 as in the case of the first primary winding 6 isclosely coupled to the secondary winding 19 which is connected in theinput circuit .of a second thermionic device 20 which functions as asecond stagefor amplifying 7571 radiofrequency currents. This inputcircuit may be traced from the grid 21 through the secondary winding 19and through the potentiometer 10 to the filament system including thecommon conductor 17 and the filament 23. A fixed condenser 8075! stageincludes the plate 24, primary winding 26 of a third radio frequencytransformer, conductor 25, the high voltage battery 16, the common Theprimary winding 26 ofthis third mentioned transformer is closely coupledto the secondary winding 2'7 thereof which is included in the inputcircuit of a detector tube 28. This input circuit is likewise tuned'by afixed condenser 28 connected in series with the common variablecondenser 13 across the input circuit in multiple with the secondarywinding 27. It will be noted that this input circuit includes the wellknown grid condenser 29 and the grid leak 30 to control the potentialspresent on the grid 31 of the detector. The filament 32 of the detectoris heated from the battery 18 as in the case of the thermionic devices 8and-20, but in this instance a variable rheostat 33 for controlling theheating of this tube is provided instead of the fixed resistancecontrols 34 5 and 35 of the other filaments. The output circuit of thedetector tube as herein shown extends from the plate 36 to an indicatingdevice 37 which may be in the form of telephone receivers or a loudspeaker. When these devices are used a well known by-pass condenser'38may beemployed. It will be understood that the indicating device 37 andthe by-pass condenser 38 may be replaced by the primary winding of anaudio transformer the secondary winding of which is connected in theinput circuit of an audio ampli-' fying thermionic device.

From the foregoing it will be understood that the input'circuits of thethermionic devices 8 and 20 and the detector tube 28 are all tuned tothe frequency of the incoming signal by means of the common variablecondenser 13 which is connected in series with the fixed condensers 12,22, and 28. All of the mentioned fixed condensers are of the samecapacity and the inductances of secondary windings 7, l9, and 2'7 areall equal,

so that any change made in the capacity of the;

variable condenser 13 causes a corresponding change in the effectivecapacity connected across the mentioned windings which changes thetuningof each input circuit and insures that, all circuits are tuned tothe same frequency over the entire band of wave lengths covered by anycombination of inductance and capacity.

It has been found in practice that such a set is especially easy tooperate since it requires the adjustment of only one variable condenserand the possible adjustment .of the potentiometer 10 in the event thatthere is any tendency for undesirable oscillations in the receiver. 4

'While the invention has been disclosed as a radio frequency amplifierin a radio receiver, it

will be understood that it may be employed for riable capacity.

, ductive reactance and a capacitive reactance conneted in eah stage,and a variable condenser in series with a, plurality of said capacitivereactances for simultaneously tuning said stages.

3; The method of tuning a multi-stage thermionic amplifier having fixedinductive reactance and fixed capacitive reactance in each stage whichconsists in adding a variable reactance supplementing said fixedreactance. r

4. The method of tuning a multi-stage amplifier havinginductance andcapacity in each stage which consists in supplementing the capacity ineach stage by common variable capacity. 5. The method of tuning amulti-stage amplifier-having inductance and capacity in a closednet-work in the input circuit of each stage which consists insupplementing the capacity in the closed net-work of each stage bycommon va- ALLAN KJRO SS.

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